This invention relates to a resin composition of a saponified product of an ethylenic copolymer. More particularly, the present invention relates to a resin composition comprising a saponified product of an ethylene-vinyl acetate copolymer which has been saponified to a high degree formulated with a specific polyamide at a specific proportion. The film or vessel molded by extrusion molding from the resin composition of the present invention is excellent in both of gas barrier characteristic and impact resistance (pinhole resistance), and is particularly suitable for use in films or vessels for packaging foods. Also, the molded product molded by injection molding of the resin composition of the present invention is excellent not only in rigidity and heat resistance but also in impact strength, and therefore useful for various functional parts as engineering plastics.
Generally speaking, saponified products of ethylene-vinyl acetate copolymer (hereinafter abbreviated as EVOH) have very good gas barrier property and therefore useful as materials for forming films or vessels for packaging foods for which oxygen gas permeability rate is required to be small. Also, compositions of EVOH formulated particularly with glass fibers have high rigidity and heat resistance, and therefore useful for various kinds of functional parts as substitute for metallic parts (Al die casting, Zn die casting, etc.).
However, the EVOH and its molding have the drawbacks that they are hard and brittle, whereby they are restricted in aspect of uses. For example, when used for films or sheets for packaging foods, the film may be broken or pinholes are liable to be formed during packaging working, moving working of packaged products or transportation working, whereby its excellent gas barrier property cannot fully be utilized. Further, in the case of utilization in injection molded products of EVOH, claims have been frequently aroused for crack generation, etc., immediately after molding and at lower temperatures.
The physical properties and moldability of EVOH will generally vary depending on the ethylene content and saponification degree. As the ethylene content is increased or the saponification degree is smaller, moldability and impact resistance can be improved, while on the contrary gas barrier property, rigidity and heat resistance will be lowered. For this reason, it has been strongly desired to have a novel technology which can improve impact strength without impairing greatly gas barrier characteristic, rigidity and heat resistance which are specific features of EVOH.
As a means for improving such drawbacks of EVOH, there have been known the method in which various kinds of polyamides are mixed with EVOH are used, as disclosed in Japanese Patent Publications Nos. 24277/1969 and 22833/1973, Japanese Unexamined Patent Publications Nos. 121347/1975, 78749/1979, 78750/1979 and 34956/1980.
According to the method as mentioned above, due to good compatibility between EVOH and polyamide, the polyamide can act so as to improve impact resistance by mixing of a polyamide with EVOH, and yet excellent gas barrier property, rigidity and heat resistance inherent in EVOH are not considerably impaired thereby.
However, the resin composition which is a mixture of EVOH and polyamide involves a great problem. That is, when EVOH and polyamide are mixed under molten state, both will undergo chemical reaction to be increased in melt viscosity until finally gelled, whereby molding becomes no longer possible.
Since such gelation becomes more marked as the molding temperature is higher, it has been proposed to use various kinds of copolymeric polyamides with lower melting temperature as the polyamide for the purpose of lower temperature molding, and such methods include those as disclosed in Japanese Unexamined Patent Publications Nos. 78749/1979, 78750/1979 and 34956/1980.
However, even according to these methods, it is difficult to prevent completely gelation and it would be desirable to have a practical method for improving impact resistance of EVOH without impairing molding processability.